Rebound hypertensive after sodium nitroprusside prevented by saralasin in rats.

The role of the renin--angiotensin system in the maintenance of blood pressure during halothane anesthesia and sodium nitroprusside (SNP)-induced hypotension was evaluated. Control rats received halothane anesthesia (1 MAC) for one hour, followed by SNP infusion, 40 microgram/kg/min, for 30 min, followed by a 30-min recovery period. A second group of rats was treated identically and, in addition, received an infusion of saralasin (a competitive inhibitor of angiotensin II) throughout the experimental period. In each group, SNP infusion resulted in an initial decrease in blood pressure from 86 torr and 83 torr, respectively, to 48 torr. During the SNP infusion the control animals demonstrated a progressive increase in blood pressure to 61 torr, whereas the saralasin-treated animals showed no change. Following discontinuation of SNP, blood pressure in the control animals rebounded to 94 torr, as compared with 78 torr in the saralasin-treated rats. This study indicates that with stable halothane anesthesia, the partial recovery of blood pressure during SNP infusion and the post-SNP rebound of blood pressure can be completely blocked by saralasin. This demonstrates the participation of the renin--angiotensin system in antagonizing the combined hypotensive effects of halothane and SNP.